Apparatuses of the above type may be used in the same way as a commonly known "joystick". The operator grasps the handle of the apparatus and thereby applies forces which, both in respect of direction and size, reproduce the move-ment which the operator wants a controlled object to perform. As a function hereof the apparatus emits signals which contain unambiguous information--both in respect of direction and size about the strain applied by the operator to the handle and which can therefore be utilized by the controlled object or by an intermediate control system for operating accordingly.
A joystick often has a substantial degree of movability and is generally used with a high translational or angular movement of the handle of the joystick that it can distinctly be felt by the operator. The emitted signal is proportional to the movement of the handle, and the joystick is most often biased by a relatively weak return spring towards its neutral position. Apparatuses of the type mentioned by way of introduction may, contrary to this, be designed in such a way that the handle is rigid or nearly rigid relative to the rest of the apparatus. A strain applied by the hand of the operator will not entail any noticeable or visible movement of the handle relative to the rest of the apparatus. Admittedly, even so rigid a construction will always move more or less when a force or a torque is applied, but the movement may be so small that it is not noticeable to the operator.
In EP-B 227,432, U.S. Pat. No. 5,222,400 and WO 93/4348 an apparatus is disclosed, in which six arms in the form of leaf springs and radially positioned in three mutually orthogonal pairs are slidably seated in the handle, the arms of each pair extending along one and the same axis and the arms in combination connecting the handle with the support.
For detecting the movements of the handle the apparatus is provided with three pairs of sensing means for sensing the translation and the rotation of the handle relative to the support. The sensing means is, with respect to each arm, provided with a light source and a light sensor which are fastened to the frame by means of suspensions, as well as a movable shutter fastened to the remote end of the arm. Each pair of sensing means can thus sense displacement of the handle relative to the frame in the direction of one axis perpendicular to the axis which connects the two means of the pair, and rotation of the handle relative to the support about a third axis perpendicular to both these axes.
Said slidable seating is a condition for the translatory movability of the handle when the arms are arranged in the above-mentioned way; the arms are in practice not deformable in their longitudinal direction, and each pair of arms would otherwise oppose translatory movement of the handle along this axis.
The slidable seating is also a prerequisite for using arms in form of leaf springs, as they are practically not deformable in the direction transverse to the longitudinal axis of the arm and transversely to the desired direction of deformation; each pair of arms which extends along the same axis would otherwise oppose both rotation of the handle about one of the axis perpendicular to said axis and translatory movement of the handle along the second one of the axes perpendicular to said axis.
Such a slidable seating has been obtained by providing the end of each leaf spring (arm) with a ball engaging a slot in the handle in the form of a slit-shaped interspace between two plane-parallel walls, said interspace having the same diameter as that of the ball and extending in the plane of the leaf spring in question.
The slidable seating of the arms is theoretically ideal in respect of providing a correct resolution of the forces and torques applied by the operator to the handle into unambiguously corresponding deflections of the six leaf springs, but entails, however, several considerable, practical drawbacks.
One considerable drawback of the construction is that it is mechanically complicated, as it consists of many mechanical components which are to be assembled when the apparatus is manufactured, which makes the manufacture difficult. In this connection, the apparatus cannot be divided into subassemblies or groups of components which in a simple way can be exchanged when repairing. The apparatus is, to judge from the publications, to be assembled from the inside and towards the outside, all its individual parts having to be mounted in a fixed order.
Another considerable drawback is that the sliding bearing, where the leaf springs engage the shell of the ball--unless it has been manufactured with a precision which is virtually unattainable--would cause an undesired mechanical play. The play may also occur under use by wear and tear of the bearing parts, a possible high precision in the bearing thus being ruined. This precision may also be ruined by the fact that apparently some of the interspaces are positioned in zones, where the ball-shaped handle is divided in two parts.
The play may i.e. cause the ball to "rattle" where it is engaging the ball shell, such that the whole construction, when exposed to vibrations, has unpredictable mechanical resonance frequencies and strong resonance oscillations. The apparatus then becomes unfit for use in a vibration-filled environment. The play may also have the effect that it becomes unclear to the user where the neutral position ends and the starting of a movement begins. Furthermore, the presence of play will have the effect that the obtained movement of the periphery of the ball as a consequence of the application of a given torque or a given force becomes bigger than it was before the play arose.
Finally, it is a substantial drawback in this prior art apparatus that, to judge from the publications, it will be very vulnerable for an unintentional overloading. Even though there seems to be rigid arms limiting the deflection of the afore-mentioned arms, this limitation takes place some distance from the ends of these movable arms, and the remote part of the arms with the ball is thus completely unprotected against overloading.
From WO-PA 95/3527 an apparatus of the same type is known, in which three arms which are placed radially in the same plane and connect the handle with the support are slidably seated in the handle.
This slidable seating is likewise a condition for translatory mobility in certain directions of the handle with this arrangement of the arms: the arms are in practice not deformable in their longitudinal direction, and each arm would otherwise oppose translatory movement of the handle along its longitudinal direction.
The slidable seating is presumably a prerequisite for unambiguously detecting the deflection of the arms. This cannot, however, be said with certainty, as the publication is very unclear in this respect.
The slidable seating has here been obtained by shaping the end of each arm (which has the shape of a thin rod) as a part of a spherical surface engaging a circular cylindrical bore with radial axis in the handle.
This slidable seating entails also in this case several considerable, practical drawbacks of the same kind as described above.
Even though this construction is less complicated than the one described above, it also comprises many mechanical elements which have to be assembled during the manufacture of the apparatus, which to judge from the publication has to take place from the inside towards the outside, all its individual parts having to be mounted in a certain order of succession.